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THE preceding papers in this series by Cuckler et al. (1956) and Cuckler and Malanga (1956) showed that nithiazide [1-ethyl-3-(5-nitro-2-thiazolyl) urea] was the most effective antihistomonad (blackhead) agent in a series of closely related compounds. Furthermore, nithiazide was found more potent and less toxic than 2-amino-5-nitrothiazole in experimental enterohepatitis. This paper presents the results of studies on the absorption and excretion of nithiazide by turkeys and chickens and the effect of this compound on their growth, maturation and reproduction. These studies have shown that chickens and turkeys tolerated nithiazide better than 2-amino-5-nitrothiazole or 2-acetylamino-5-nitrothiazole, chemically related compounds. MATERIALS AND METHODS The turkeys and chickens used in these studies were obtained from commercial sources when 1 day of age. Straight run Beltsville White turkeys and White Rock cross chicks were used in the laboratory experiments, and the birds were kept in electrically heated battery brooders. The floor-pen growth trials involved White . . .

Summary1. The data presented show that nithiazide [1-ethyl-3-(5-nitro-2-thi-azolyl) urea | was more potent and less toxic than 2-amino-5-nitrothiazole when fed to turkeys with enterohepatitis. 2. Nithiazide was most effective when administered prior to infection or beginning 3 to 7 days after infection. It prevented mortality from enterohepatitis produced either by oral exposure to cecal worm eggs or by rectal inoculation of Histomonas meleagridis cultures. Nithiazide may be administered in the feed or water and is equally effective in either form. 3. The therapeutic feeding of rations containing 0.05% nithiazide, starting 3 days after infection, prevented mortality from infectious enterohepatitis which was lethal for 73% to 83% of the untreated control turkeys.

Summary1. The preparation of 1-mono-substituted and 1,1-disubstituted nitrothia-zolylureas has been described. 2. Antihisto-monad activity was demonstrated for mono-substituted thiazolylureas with not more than 4 carbon atoms. The 1-methyl compound was more toxic and less effective than the 1-ethyl derivative. The dimethyl compound was less toxic and also less effective than the mono-methyl compound. 3. In addition to therapeutic activity in enterohepatitis, nithi-azide [l-ethyl-3-(5-nitro-2-thiazolyl) urea] was found to have antitrichomonal activity but antimalarial, antitrypanosomal or anticoc-cidial activity was not demonstrable.